RIBD is a radioisotope buildup and decay code designed to analyze the fission product content of irradiated reactor fuel in terms of potential biological hazards and heating effects accompanying radioactive decay.

RIBD is a grid processor which calculates isotopic concentrations resulting from two fission sources with normal down-chain decay by beta emission and isomeric transfer and inter-chain coupling resulting from (n,gamma) reactions. The calculations follow the irradiation history through an unlimited number of step changes of unrestricted duration and variability including shutdown periods, restarts at different power levels and/or any other level changes.
A nuclear data library has been generated for use with RIBD to calculate fission product inventories and decay heat rates associated with fuels irradiated in fast reactor environments.